The present invention relates to a method and apparatus for controlling a supply of oxygen delivered to a human.
There are many instances in which it is desirable, if not necessary, to deliver oxygen to a human. Many of such instances include that where supplemental oxygen is necessary due to medical exigency. Other instances include that where a human is subject to breathing oxygen-depleted air, such as when flying or mountain climbing at high altitudes.
There are a variety of systems for delivering oxygen to a human. Many of the systems are of the so-called xe2x80x9cclosed loopxe2x80x9d breathing systems. In closed-loop breathing systems, the gas which a user breathes is entirely supplied to the user through the system, the user not breathing any gas directly from the atmosphere. Such systems include ventilators.
On the other hand, there are systems of the so-called xe2x80x9copen-loopxe2x80x9d breathing system. In such systems, a portion of the gas which a user breathes is obtained directly from the atmosphere, and the remaining portion is supplied to the user. These systems have the advantage of generally being less complicated than closed-loop breathing systems, both when considering the apparatus and the control strategy. In particular, an open-loop breathing system may comprise as little as an oxygen supply. The simplicity of the open-loop breathing system makes the system especially desirable for use in situations where space and weight are significant factors, such as in aviation and mountain climbing.
Nonetheless, current open-loop breathing systems suffer from numerous drawbacks. Given the weight and space constraints of aviation and similar environments, it is critical to control the oxygen delivery to the user so that the oxygen which is delivered is used by the user, and is necessary for use by the user. For example, in an open-loop system, oxygen may be delivered to the user continuously, whether or not the user has a need for it from a blood-oxygen standpoint, and whether or not the user is breathing at the time the oxygen is being delivered. This wastes oxygen, making it necessary to provide a much greater oxygen supply than the user actually needs. Providing additional tanks of oxygen adds weight and occupies additional space.
Several schemes have been proposed for controlling oxygen delivery. One early system is that described in U.S. Pat. No. 2,414,747 to Kirschbaum. This patent contains a disclosure of a system in which a person""s blood-oxygen level is monitored to control an oxygen supply. The device described therein is quite rudimentary, however, and suffers from a number of drawbacks. A first problem is that the device uses a mechanically complex motor drive arrangement for controlling the flow of oxygen. This drive makes the device large and heavy. In addition, the system does not address the needs of the user when considering the range of blood-saturation levels and breathing patterns.
Other more complex systems have been proposed. For example, U.S. Pat. No. 5,365,922 to Raemer discloses an oxygen saturation control system. As described therein, this system is for use in a closed-loop breathing system employing a ventilator. This system is overly complex because of its application to the closed-loop breathing system, as it will be appreciated that in such systems, great care must be taken to ensure that the fraction amount of oxygen delivered to the patient to prevent oxygen overdose/underdose. This is especially the case in a closed-loop breathing system since the only oxygen which is delivered to the patient is through the system (i.e. the oxygen is not supplemental to that of normal atmospheric breathing, as in the case of an open-loop system). In the arrangement described, xe2x80x9cpseudoxe2x80x9d blood-saturation signals are generated and a control responsive to the pseudo signal sets a fraction amount of oxygen delivered to the patient.
An oxygen delivery control in an xe2x80x9copenxe2x80x9d-loop type breathing system which overcomes the above-stated problems is desired.
The present invention comprises an oxygen delivery control apparatus and method.
In one embodiment of the invention, the oxygen delivery control apparatus is arranged to control the flow of oxygen to a user in an open-loop breathing system including an oxygen supply and a delivery apparatus for delivering supplemental oxygen to a user. In one embodiment, this apparatus comprises a valve provided along an oxygen delivery path between the oxygen supply and the delivery apparatus, the valve having a first position permitting oxygen to flow from the supply to the delivery apparatus, and a second position preventing oxygen from flowing from the supply to the delivery apparatus; a pressure sensor associated with the valve and arranged to detect a period of inhalation by the user by detecting a condition of reduced pressure associated with the apparatus for delivering supplemental oxygen to a user; an oximeter arranged to measure a blood-oxygen saturation level of a user and provide an output signal indicative of the same; and a processor for controlling the valve so as to cause the valve to move to the first position and cause oxygen to be delivered to the user when the output signal from the oximeter indicates a blood-oxygen saturation which is below a selected blood-oxygen saturation level and a condition of inhalation is detected by the pressure sensor.
One or more embodiments of the invention comprise methods for controlling a supply of oxygen to a user. One embodiment comprises a method of controlling the flow of supplemental oxygen from an oxygen supply to a user through a delivery apparatus in an open-loop breathing system, the delivery apparatus including a valve moveable between a first position permitting oxygen to flow from the supply to the user and a second position for preventing oxygen to flow from the supply to the user, comprising the steps of determining a blood-oxygen saturation level of a user; determining the existence of a condition of inhalation by a user; determining if the user requires supplemental oxygen; in the event the user requires supplemental oxygen, determining a length of time the valve should be moved to the first position in order to deliver a desired quantity of oxygen; moving the valve from the second position to the first position for the length of time; and returning the valve to the first position.
In one or more embodiments, oxygen is delivered to a user in accordance with a specific control strategy. In one embodiment, the control strategy for an apparatus controlling the flow of oxygen from an oxygen supply to a user comprises determining a desired blood-saturation goal level; determining an actual blood-saturation level for the user; determining a minimum blood-saturation level for the user; providing a maximum amount of oxygen to the user if the goal has not been reached and the current level is below the goal level; providing a maximum amount of oxygen to the user if the goal has been reached but the actual level is below the minimum level; providing an amount of oxygen based on an assigned functional relationship between oxygen amount and blood-oxygen content level if the goal has been reached but the actual level is below the minimum level; and providing at least a minimum amount of oxygen if the actual level is above the goal level.
Further objects, features, and advantages of the present invention over the prior art will become apparent from the detailed description of the drawings which follows, when considered with the attached figures.